No two yeasts are the same.
Some are dominant, some arent.
Some contribute more aromatic notes
Some bring more mouthfeel/body
Some highlight certain characteristics - spice, fruit, etc
Some take more nutrients than others
Some make more SO2 than others - can impact the MLF-ability of the wine post-ferment
Some have higher ABV tolerances
They've all been isolated from different areas - France, Germany, Italy, Austrailia, California - and yeasts from these different regions tend to lend well to those area's traditional styles
When you take all these different facets, and align them with the fermentation you have in mind, you can start to see how some of the more "traditional" yeast blends have came to be...
Like D254 + D80, in 'larger' red wines
Or say you're making a fruit wine (Apple?), and you want a decent amount of body from the yeast, but also want to reduce malic acid content and enhance the fruity aromas of the wine.. What to do?
Split the batch per your % of fruity-to-mouthfeel
Pitch 71B-1122 for malic acid reduction and enhancement of fruity esters
Pitch D-47 for its mouthfeel/body enhancing ability
Both have roughly the same ABV & nutritional requirements
D-47 doesnt create enough SO2 to inhibit MLF
When you blend them correctly, you end up with the 'best of both worlds' - fruity aromatics, a slightly reduced malic sharpness, enhanced body/mouthfeel texture, the ability to follow-up with MLF if malic acid wasnt reduced enough..
This is just a simple example... But you can see how learning about as many different yeast strains as you can, is just adding more tools to your toolbox, as Joe would say.
